An exhaust gas cleaning system using a ceramic catalytic converter is known as means for removing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) and the like that are included in exhaust gas from automobile engines. Basically, the ceramic catalytic converter generally stores a ceramic catalyst carrier with a honeycomb shape or the like in a metal casing.
There are various types of ceramic catalytic converters, but a general form provides a catalyst carrier, a casing that stores the catalyst carrier, and a thermal insulation member that fills a gap between the outer surface of the catalyst carrier and the inner surface of the casing. The thermal insulation member mounts the catalyst carrier and prevents mechanical shock due to impact and vibration and the like from being inadvertently applied to the catalyst carrier. Thereby, moving and breaking of the catalyst carrier can be sufficiently suppressed, and thus the desired effect can be provided over a long period of time. This type of thermal insulation member is also commonly called a mounting member because the member has a function of mounting a pollution control element such as a catalyst carrier.
Japanese Unexamined Patent Applications Publication Nos. S57-61686 and 2002-66331 teach that, normally, the mounting member is primarily made of inorganic fibers, from the prospect of providing excellent thermal insulation and heat resistance. However, inorganic fibers can scatter broken pieces and powder and the like (hereinafter also referred to as “fiber pieces”) when the pollution control element is assembled in the casing, and there is a possibility of having a negative effect on the surrounding environment. Therefore, conventionally there have been investigations into impregnating or applying an organic binder onto a mat made of inorganic fibers in order to prevent scattering of the fiber pieces. For example, Japanese Unexamined Patent Application Publication No. 2006-223920 describes a mounting member where at least two types of organic binders with different glass transition temperatures (Tg) are impregnated into a mat made of fiber materials.